Voltage regulator



E. MITTELMANN VOLTAGE n REGULATOR Filed March 13, 1946 Nov., 22, 1949 FIVE' "IVLVA 7b Powe/1 4m @www `Patented Nov. 22, 1949 VOLTAGE REGULATOR Eugene Mittelmann, Chicago, lli., assignor to Illlnois Tool Works, Chicago, Ill., a corporation of Illinois Application March 13, 1946, Serial No. 654,200

4 Claims.

The present invention relates to an apparatus and method for maintaining substantially constant nlament voltage for an electronic power tube.A

High power electronic or vacuum tubes, such as used in high frecuency heating apparatus and in radio transmitters, require a relatively large amount of filament power. A constant voltage power transformer capable of handling that amount of power is quite expensive.

The present invention contemplates the use of a regulatory control circuit by which deviations from a constant voltage supplied vby a low power voltage transformer are compared by a bridge circuit to a voltage supplied by a variable voltage high power transformer to control the voltage applied by the high power transformer to the filaments of the electronic tubes.

It is, therefore, an object of the present invention to provide an improved apparatus and method for maintaining substantially constant the iilamentjvoltage of electronic power tubes.

Other and further objects of the present invention will become apparent by reference to the Yfollowing descriptiontaken in connection with the accompanying drawing wherein the single figure is a schematic diagram of a control circuit for regulating the filament supply voltage for electronic power tubes.

In accordance with 'the present invention the nlamentsupply voltage for the electronic power tubes is controlled by an adjustable, variable voltage power transformer, or other variable voltage supply device, which is adjusted by a control circuit. This control circuit utilizes two vacnum tubes Vl and V2 arranged in` a bridgev circuit including anode resistors Zi and Z2 connected between the anodes of the vacuum tubes Vi and V2 and the positive terminal of a source of anode voltage.

The vacuum tubes Vi and V2 may have a common cathode bias resistor Z connected to ground. Between the balance points of the bridge circuit which are located at the anodes of the vacuum tubes Vi and V2 there are connected two circuits including relays Rl and R2. The circuit including the relay RI includes a unilaterally conductive device or contact rectier CRI. Another circuit includes the relay R2 and another similar contact rectifier CRZ connected to be conductive in the opposite direction to rectifier CRI.

The grid of the vacuum tube VI is provided with a grounded grid resistor Z3. The grid is connected to a unilaterally conductive device such as a contact rectler CR3 which is connected to one terminal of a voltage divider or potentiometer Pl having its movable contact connected to ground. The voltage divider Pl is arranged so as normally to be in parallel with the secondary winding W2 of a small, low current constant voltage transformer Tl having a primary winding Wi formed in two sections separated by a shunt core member. The transformer TI may however be of any other suitable type of constant voltage transformer.

One portion of the primary winding WI is closely coupled to the secondary winding W2 and the other portion of the primary winding WI is closely coupled to a tertiary winding W3 which is shunted by a `capacitor C. I'he primary winding of the transformer Tl is energized from alternating current conductors Ll and L2.

The vacuum tube V2 is provided with a grounded grid resistor Z4 and the grid is connected to a contact rectier CR! vThe contact rectifier CRA is connected to one terminall ofA a voltage divider or potentiometer P2 having its adiustable contact connected to ground. The voltage divider PZ is connected across a secondary winding of a transformer T2 which is energized from the output of a transformer T.

The transformer T is of the variable voltage type and has an adjustable contact which is moved to the proper position by a motor controlled in accordance with the operation of the vacuum tubes VI and V2. The transformer T is connected across the alternating current lines LI and L2 and supplies energy to the transformer T2 and a transformer T3 having its secondary winding connected to the filament circuit of the power tubes. The transformer 12 therefore supplies to the grid circuit of the vacuum tube V2 a voltage proportional to the voltage supplied to the filaments of the power tubes.

The adjustable contact on the transformer T is actuated by a motor FM which has two inductive windings FMI and PM2 and two capacitors FMS and FMQ. The common juncture between the two capacitors is connected to one of the alternating current lines such as .LI and also to one of each of the pairs of contacts of the relays RI and R2. The common juncture between the inductive windings FMI and FMZ is connected through a limit switch S3 to the other alternating currentconductor L2.

'Ihe limit switch S3 is positioned so that it will be opened when the adjustable contact on the transformer T is moved toa position Where the transformer no longer supplies sufllcient output voltage. The limit switch S3 is connected in parallel with the normally open contacts S2 of the manually operable switch S. The manually operable switch S which may be of the push button type is also provided with another pair of normally open contacts SI. The normally open contacts SI are connected in parallel with the normally open contacts of a relay PR.

The relay PR is arranged to be energized in accordance with the conventional on-and-off control circuits (not shown) of the power tubes. Upon conditioning the power tubes for operation, the relay PR is operated to close its contacts and connect one terminal of the secondary winding of the transformer W2 to the voltage divider or potentiometer PI.

The circuit shown operates to compare the constant voltage supplied by the secondary winding W2 of the transformer TI with the voltage supplied to the transformer T2. The secondary winding W2 of the transformer Tl is arranged to supply a constant voltage proportional to the voltage which is normally to be supplied to the filament circuit of the power tubes.

The voltage divider PI is provided to adjustably preset the proportional amount of the constant valued voltage which is applied to the vacuum tube VI Similarly an adjustably presettable, proportional amount of the alternating current output voltage of the transformer T2 is applied through the voltage divider P2 to the grid of the vacuum tube V2. An increase in the control voltage of the grid circuit of V2 will cause the relay R2 to be operated which thereby will close its contacts to cause the motor FM to move the adjustable contact on the transformer T until the voltages supplied to the two vacuum tubes VI and V2 are again balanced.

Similarly if the voltage applied to the grid circuit of the vacuum tube V2 is less than that applied to the grid circuit of the vacuum tube VI, the relay RI will be actuated so that its contacts cause the motor circuit FM to close to cause the adjustable contact on the transformer to move in the opposite direction until the balanced condition has been restored.

If desired, an increased tube life may be obtained by reducing the voltage supplied to the laments of the power tubes by the transformer T3 to a value somewhat under the rated value. This can be accomplished by adjustment of the voltage dividers PI or P2. Of course any other desired level of constant filament voltage may be obtained. The voltage divider PI, for example, has a certain portion thereon connected in series with a circuit including the contact rectifier CRB and the impedance Z3 so that a certain direct current bias is applied to the grid of the vacuum tube VI. The grid of the vacuum tube V2 is similarly supplied with direct current bias which varies in accordance with the potential output of the transformer T2.

The circuit for the automatic control of the output voltage of the transformer T is normally inoperative until the power tube equipment which it is associated with is placed in operation so that the control circuits therefor operate the relay PR to close its contacts. The contacts of the relay PR will set the circuit for automatic operation. In order initially to set the filament voltage before the high tension voltages are applied to the power tubes, the manual switch S is actuated. Actuation of the switch S closes the switch contacts SI so as to connect the secondary winding W2 of the transformer Tl to the voltage divider Pl. Operation of the switch S also closes contacts S2 so that a circuit is prepared for the motor FM if the limit switch S3 is open.

I'he closing of the switch S therefore supplies power to the vacuum tube VI which causes the relay R2 to close its contacts thereby to initiate operation of the motor FM which moves the adjustable contact on the transformer T away from the limit position. When the adjustable contact on the transformer T has been moved to a position where the output voltage of that transformer is in the preset proportion to the output voltage of the secondary winding W2 of the transformer TI, the vacuum tube V3 will have a grid circuit potential such that the relay R2 is deenergized. 'Ihe relays RI and R2 operate only as long as a potential difference exists between the balance points of the bridge which are located at the anodes of the two vacuum tubes VI and V2. The push button switch thereupon may be released. When, thereafter, the control circuits associated with the power tubes are energized, the relay PR will be actuated and the filament voltage will automatically be maintained constant.

Whenever the power tube equipment is shut down, the relay PR will open its contacts thereby removing the grid bias from the vacuum tube VI and thus leaving the vacuum tube V2 energized. This condition causes the relay Rl to become closed so as to actuate the motor FM which will then move the adjustable contact on the transformer T back to its zero or preset lowvalued position. At that position an adjustaable abutment (not shown) on the adjuster for the transformer T opens the limit switch S3 thereby deenergizing the motor FM.

The circuit shown is connected to alternating current lines LI and L2 at a point in advance of the usual high tension control switches for the power tube equipment so that upon interruption of the operation of the vacuum tube apparatus, control voltages will be supplied to the circuit shown to permit the circuit to be restored to its no-load condition.

From the foregoing it will readily become apparent to those skilled in the art that the device of the present invention is capable of handling a large amount of power without the use of relatively expensive or heavy constant voltage equipment. While the device for controlling the voltage output has been shown as being an adjustable tap transformer T, it will be understood that other adjustable voltage supply devices might be used in place thereof.

While for the purpose of describing and explaining the present invention, a single embodiment has been shown in the drawing, it is to be understood that such variations and modifications thereof are contemplated as may be commensurate with the spirit and scope of the invention defined in the appended claims.

This invention is hereby claimed as follows:

l. The combination for supplying substantially constant alternating current voltage to a load comprising a source of alternating current, adjustable voltage power means interposed between said source and said load, a motor for adjusting said device, a balanced bridge control circuit for controlling the operation of said motor, means for supplying to said bridge circuit a potential proportional to the potential supplied to said load, and means for supplying to said bridge circuit a constant potential alternating current having a value equal to the rated voltage to be supplied to said load.

2. An apparatus for supplying power to the iilaments of vacuum tubes at substantially constant potential comprising a source of alternating current, a variable voltage power transformer having voltage adjustment means and connected to said source of alternating current for supplying power to said laments, a motor for adjusting the position of said adjustment means, a bridge circuit for controlling the operation oi said motor, a connection between said power transformer and one arm-of the bridge circuit to supply thereto a voltage proportional to the voltage applied to the filaments by said power transformer, a constant voltage transformer connected to said alternating current source, the vconstant voltage transformer having a secondary winding arranged to supply to another arm of the bridge circuit a voltage proportional to the rated lament voltage of said vacuum tubes, a relay having a pair of contacts interposed between said bridge circuit and said constant transformer, said relay being adapted to be connected to the control circuit of the power tubes to energize and deenergize the last mentioned arm of the bridge circuit in response to the control circuit of the power tubes, a limit switch arranged to be opened by the adjustment means of said power transformer at a preset low voltage output position, Aand manually operable switch means for bridging the contacts of said limit switch and the contacts of said relay manually to preset the adjustment means of the power transformer prior to the operation of the power tubes.

3. In a system for supplying relatively large power at a substantially constant alternating current voltage from a source of alternating current subject to voltage variations, the combination comprising a circuit having an input, an output, and voltage adjustable means connected therebetween, said voltage adjustable means having mechanically operable adjustment means, a motor for adjusting said adjustment means, a

space discharge tube bridge circuit having a pair of space discharge tubes, means for supplying to one of said space discharge tubes a potential proportional to the potential supplied to said output, means for deriving from said input a constant valued potential proportional to the predetermined value of the voltage desired to be supplied by said output, means for supplying said constant valued potential to the other of said tubes, and means responsive -to said bridge circuit for controlling the direction and extent of rotation of said motor in accordance with the direction and extent of deviation of the voltage of said output from said predetermined value.

t. 'The combination for supplying power at substantially constant alternating current voltage to a load comprising a supply source of alternating current of high power, means for supplying a constant voltage alternating current of low power, equal in voltage to the voltage of the A. C. power to be supplied to the load, adjustable means for supplying power to the load from said source of alternating current of high power, means for comparing the alternating current voltage applied to the load from the high power source with said constant alternating current voltage of low power, and means for continuously adjusting said adjustable means in response to the diierence of the comparison to maintain substantially constant the voltage of the alternating current applied to said load from the high power source.

EUGENE MIT'I'ELMANN.

REFERENCES CITED The following references are of record in the nie of this patent:

UNTED STATES PATENTS Number Name Date 2,239,758 Artzt Apr. 29, 1941 2,368,582 Sziklai Jan. 30, 1945 

